Btrfs: btrfs_lookup_dir_item() can return ERR_PTR

btrfs_lookup_dir_item() can return either ERR_PTRs or null.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/ioctl.c

@@ -1845,7 +1845,7 @@ static long btrfs_ioctl_default_subvol(struct file *file, void __user *argp)
 	dir_id = btrfs_super_root_dir(&root->fs_info->super_copy);
 	di = btrfs_lookup_dir_item(trans, root->fs_info->tree_root, path,
 				   dir_id, "default", 7, 1);
-	if (!di) {
+	if (IS_ERR_OR_NULL(di)) {
 		btrfs_free_path(path);
 		btrfs_end_transaction(trans, root);
 		printk(KERN_ERR "Umm, you don't have the default dir item, "